ActiveStorage reflection

activerecord/lib/active_record/reflection.rb

@@ -13,33 +13,37 @@ module Reflection # :nodoc:
       class_attribute :aggregate_reflections, instance_writer: false, default: {}
     end
 
-    def self.create(macro, name, scope, options, ar)
-      klass = \
-        case macro
-        when :composed_of
-          AggregateReflection
-        when :has_many
-          HasManyReflection
-        when :has_one
-          HasOneReflection
-        when :belongs_to
-          BelongsToReflection
-        else
-          raise "Unsupported Macro: #{macro}"
-        end
+    class << self
+      def create(macro, name, scope, options, ar)
+        reflection = reflection_class_for(macro).new(name, scope, options, ar)
+        options[:through] ? ThroughReflection.new(reflection) : reflection
+      end
 
-      reflection = klass.new(name, scope, options, ar)
-      options[:through] ? ThroughReflection.new(reflection) : reflection
-    end
+      def add_reflection(ar, name, reflection)
+        ar.clear_reflections_cache
+        name = name.to_s
+        ar._reflections = ar._reflections.except(name).merge!(name => reflection)
+      end
 
-    def self.add_reflection(ar, name, reflection)
-      ar.clear_reflections_cache
-      name = name.to_s
-      ar._reflections = ar._reflections.except(name).merge!(name => reflection)
-    end
+      def add_aggregate_reflection(ar, name, reflection)
+        ar.aggregate_reflections = ar.aggregate_reflections.merge(name.to_s => reflection)
+      end
 
-    def self.add_aggregate_reflection(ar, name, reflection)
-      ar.aggregate_reflections = ar.aggregate_reflections.merge(name.to_s => reflection)
+      private
+        def reflection_class_for(macro)
+          case macro
+          when :composed_of
+            AggregateReflection
+          when :has_many
+            HasManyReflection
+          when :has_one
+            HasOneReflection
+          when :belongs_to
+            BelongsToReflection
+          else
+            raise "Unsupported Macro: #{macro}"
+          end
+        end
     end
 
     # \Reflection enables the ability to examine the associations and aggregations of

activestorage/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Add the ability to reflect on defined attachments using the existing
+    ActiveRecord reflection mechanism.
+
+    *Kevin Deisz*
+
 *   Variant arguments of `false` or `nil` will no longer be passed to the
     processor. For example, the following will not have the monochrome
     variation applied:

activestorage/lib/active_storage/attached/macros.rb

@@ -48,6 +48,12 @@ def #{name}=(attachable)
       else
         before_destroy { public_send(name).detach }
       end
+
+      ActiveRecord::Reflection.add_attachment_reflection(
+        self,
+        name,
+        ActiveRecord::Reflection.create(:has_one_attached, name, nil, { dependent: dependent }, self)
+      )
     end
 
     # Specifies the relation between multiple attachments and the model.
@@ -105,6 +111,12 @@ def purge_later
       else
         before_destroy { public_send(name).detach }
       end
+
+      ActiveRecord::Reflection.add_attachment_reflection(
+        self,
+        name,
+        ActiveRecord::Reflection.create(:has_many_attached, name, nil, { dependent: dependent }, self)
+      )
     end
   end
 end

activestorage/lib/active_storage/engine.rb

@@ -10,6 +10,8 @@
 require "active_storage/analyzer/image_analyzer"
 require "active_storage/analyzer/video_analyzer"
 
+require "active_storage/reflection"
+
 module ActiveStorage
   class Engine < Rails::Engine # :nodoc:
     isolate_namespace ActiveStorage
@@ -95,5 +97,12 @@ class Engine < Rails::Engine # :nodoc:
         end
       end
     end
+
+    initializer "active_storage.reflection" do
+      ActiveSupport.on_load(:active_record) do
+        include Reflection::ActiveRecordExtensions
+        ActiveRecord::Reflection.singleton_class.prepend(Reflection::ReflectionExtension)
+      end
+    end
   end
 end

activestorage/lib/active_storage/reflection.rb

@@ -0,0 +1,64 @@
+# frozen_string_literal: true
+
+module ActiveStorage
+  module Reflection
+    # Holds all the metadata about a has_one_attached attachment as it was
+    # specified in the Active Record class.
+    class HasOneAttachedReflection < ActiveRecord::Reflection::MacroReflection #:nodoc:
+      def macro
+        :has_one_attached
+      end
+    end
+
+    # Holds all the metadata about a has_many_attached attachment as it was
+    # specified in the Active Record class.
+    class HasManyAttachedReflection < ActiveRecord::Reflection::MacroReflection #:nodoc:
+      def macro
+        :has_many_attached
+      end
+    end
+
+    module ReflectionExtension # :nodoc:
+      def add_attachment_reflection(ar, name, reflection)
+        ar.attachment_reflections.merge!(name.to_s => reflection)
+      end
+
+      private
+        def reflection_class_for(macro)
+          case macro
+          when :has_one_attached
+            HasOneAttachedReflection
+          when :has_many_attached
+            HasManyAttachedReflection
+          else
+            super
+          end
+        end
+    end
+
+    module ActiveRecordExtensions
+      extend ActiveSupport::Concern
+
+      included do
+        class_attribute :attachment_reflections, instance_writer: false, default: {}
+      end
+
+      module ClassMethods
+        # Returns an array of reflection objects for all the attachments in the
+        # class.
+        def reflect_on_all_attachments
+          attachment_reflections.values
+        end
+
+        # Returns the reflection object for the named +attachment+.
+        #
+        #    User.reflect_on_attachment(:avatar)
+        #    # => the avatar reflection
+        #
+        def reflect_on_attachment(attachment)
+          attachment_reflections[attachment.to_s]
+        end
+      end
+    end
+  end
+end

activestorage/test/models/reflection_test.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class ActiveStorage::ReflectionTest < ActiveSupport::TestCase
+  test "allows reflecting for all attachment" do
+    expected_classes =
+      User.reflect_on_all_attachments.all? do |reflection|
+        reflection.is_a?(ActiveStorage::Reflection::HasOneAttachedReflection) ||
+          reflection.is_a?(ActiveStorage::Reflection::HasManyAttachedReflection)
+      end
+
+    assert expected_classes
+  end
+
+  test "allows reflecting on a singular has_one_attached attachment" do
+    reflection = User.reflect_on_attachment(:avatar)
+
+    assert_equal :avatar, reflection.name
+    assert_equal :has_one_attached, reflection.macro
+  end
+
+  test "allows reflecting on a singular has_many_attached attachment" do
+    reflection = User.reflect_on_attachment(:highlights)
+
+    assert_equal :highlights, reflection.name
+    assert_equal :has_many_attached, reflection.macro
+  end
+end